The Social Brain

Question 1

Brain size

Answer 1

Body weight increases quicker than brain weight (Roth & Dicke, 2005).

• brains of hominoids evolved faster than apes.
• homosapiens have largest relative brain size.

Special case primates:

• evolvement of large brains happened to all vertebrate taxa.
• but social brain hypothesis different in other mammals and birds.
• eg. bird brain size related to pair bonding.

Humans/primates = related to stable relationships and social network size (Shultze & Dunbar, 2007).
- possibly due to cognitive demands of sociality placing a constraint on number of people that can be maintained in a coherent group (Dunbar, 2009).

Question 2

Evolvement of the neocortex: (NC + allocortex = cerebral cortex)

Answer 2

Neocortex = largest and outer part of the cerebral cortex covering two hemispheres.
- responsible for higher functions.

Allocortex = smaller, mainly olfactory system and hippocampus.

Question 3

Evolvement of the neocortex: neocortex

Answer 3

Evolution of the brain:

• reptilian brain -> mammalian brain -> neocortex.
• breathing/hunger/temperature -> memory/love/anxiety/sociality/fear -> logic/language/morality/emotional control etc.

Functions: survival -> adaptation to environment -> high functions.

Neocortex is necessary for high social functions - our most powerful “tool”.

Question 4

Evolvement of the neocortex: cost of a large brain

Answer 4

Brain responsible for 22% resting energy expenditure (McClave & Snider, 2001).

• 2/3 of neural firing; 1/3 for maintenance.
• some say that liver costs more.

Question 5

Evolvement of the neocortex: evolution of the neocortex

Answer 5

Needs large brain to support it.

Large brain demands sufficient energy supply (nutritious diet).
- some argue that the use of fire improved nutrition intake and is a key factor in human evolution.

Social brain can benefit the species and offset extra energy demand (Dunbar & Shultz, 2007).

Question 6

Social brain hypothesis

Answer 6

Proposed by Dunbar - argues human intelligence did not evolve primarily as a means of ecological problems, but instead as a means of survival and reproducing in large social groups.

Question 7

Brain and social networks: neocortex in primates

Answer 7

Neocortex: accounts for most of the differences between living primate taxa (Stephan, 1972; Passingham, 1982).

Sociality: Our evolutionary goal.

Question 8

Brain and social networks: neocortex ratio (in comparison to rest of brain)

Answer 8

Neocortex ratio (CR) = NC volume / (brain volume - NC volume)

In humans NC volume = 1006.5cc.
Total brain volume = 1251.8cc (Stephen et al, 1981).

About 50% larger than the max value for any other primate species (Dunbar, 1992).

Question 9

Brain and social networks: ecological or social?

Answer 9

Primates have larger brains because:

Ecological theory (eg. Gibson, 1986) - large brains provide ecological functions of cognitive skills.
- especially in large ecologically flexible species like primates.
(OR)
Social theory (eg. Byrne & Whiten, 1988) - large brains mainly for social function to intellect, emphasising uniquely complex nature of primate social life.

Question 10

Brain and social networks: Dunbar’s work

Answer 10

Data on neocortex volume, group size and other behavioural ecology variables (body mass, fruit in diet, activity etc) collected from 38 primate taxa correlated (Dunbar, 1992).

• group size positively correlated with CR - SUPPORTING SOCIAL INTELLECT THEORY.
• number of relationships able to monitor simultaneously is limited by size of neocortex.
• group over this limit is unstable.

Question 11

Brain and social networks: grooming is a social activity

Answer 11

Social animals adapt grooming behaviours to bond and strengthen social structures.

Plays important role in forming social bonds in many primate species.

Question 12

Brain and social networks: social network size

Answer 12

In primates large groups are created by welding together sets of smaller grooming cliques (Dunbar, 1992).
- clique sizes correlated significantly with CR in primates (Kudo & Dunbar, 2001).

Question 13

Brain and social networks: Dunbar’s number

Answer 13

CR vs group size (Dunbar, 1992; 2003)
- steeper increase in apes than monkeys.

Dunbar extrapolated the correlation and suggested a number of 148 for effective human social group size.

• rounded to 150 = Dunbar’s number.
• 231 = Bernard-Killiworth’s number (1987) - not as popular.

Question 14

Brain and social networks: social groups

Answer 14

Predicted social group size for hominoid populations using regression.

Group size increased during primate evolution (Dunbar, 2003).

Question 15

Brain and social networks: interpreting Dunbar’s number

Answer 15

“Number of people you wouldn’t mind joining uninvited if you bumped into them” - Dunbar, 1998.

Social brain hypothesis often formulated in terms of this number.

But is more correct to think of as a measure of complexity of social relationships.

Relationships need maintenance, consuming energy and time, thus require a more developed brain.

Question 16

Social networks in humans: human society

Answer 16

Dunbar’s number is an estimation - needs to be checked.

Question 17

Social networks in humans: using Dunbar’s number

Answer 17

W.L Gore & Associates - buildings accommodate 150 employees.

Swedish tax authority - organised offices max 150 per office.

Any group greater than 150 - becomes dysfunctional.

• company size = 75-200.
• organisations > 150 need bureaucracy.

Question 18

Social networks in humans: social group layers

Answer 18

Support clique: people we seek personal advice from.

Sympathy group: special ties, frequent contact.

Band: acquaintances, less frequent.

Clan: all current contacts.

Megaband & tribe: larger social units.

Closeness and mean time spent interacting with individuals decreases in each layer as the number in the social group increases (Sutcliffe et al, 2012)

Question 19

Social networks in humans: the expanding circles

Answer 19

Our relationships form a hierarchically inclusive series of increasing size but decreasing intensity (i.e. quality of relationship).

• 150 = limited reciprocated relationships.
• 1500 = limit on memory for faces?

Each circle is 3X larger than the one inside of it (Dunbar, 2014; Roberts, 2010).

Question 20

Social networks in humans: social media

Answer 20

Can we have a larger network online? - no.

With online group size similar to f-to-f networks (Dunbar, 2012;2016).

Relationship quality suffers without f-to-f interaction.

Similar results found for mobile phone networks (Miritello et al, 2013).

Question 21

Social time: Mind the gap: why is it important?

Answer 21

Grooming as the bonding agent in primates.

• grooming time determined by group size.
• upper limit about 20% of total daytime.

Question 22

Social time: social grooming in humans

Answer 22

Humans version = conversation.

Mechanism of social bonding: 60% of conversation is to social topics (eg. gossiping; Dunbar, 1993/2004).

Similar to primates - social grooming.

Language evolvement = gossiping.

Question 23

Social time: bridging the gap

Answer 23

Religion and its rituals.
Music and dance.
Laughter - trait shared with chimps.

Question 24

Social time: how grooming works

Answer 24

Music and laughter triggers endorphin uptake (Dunbar, 2012a;b).
- endorphins are relaxing.

Create psycho-pharmacological environment for building trust?

Question 25

Individual differences: general cognitive abilities

Answer 25

Problem solving: animals with larger brain volume are more capable (Benson-Amram et al, 2016).

Maintenance of social networks requires cognitive functioning - eg. memory.

Question 26

Individual differences: clique sizes

Answer 26

Size of support clique: innermost circle - predicted y mentalising skills (Stiller & Dunbar, 2007).

Size of sympathy group: most frequent social partners - predicted /explained by memory performance.

Question 27

Individual differences: sociality

Answer 27

Correlated sociality to brain structure sizes, with body differences and age controlled (Horvath et al, 2011).

Measured sociability using Zuckerman-Kuhlman Personality Questionnaire form III (Zuckerman et al, 2002).
- sociability scores vs. temporal lobe size.

Question 28

Individual differences: benefit of sociality

Answer 28

Problem solving is more effective socially than individually.
- requires high level of sociality.

The benefit of sociality for general cognition and creativity outweighs the cost for maintaining a large brain (Dunbar & Shultz, 2007).

Question 29

Individual differences: monkey temporal lobe/PFC

Answer 29

Social group sizes predicted by grey matter density in PFC in macaques (Sallet et al, 2012).

Question 30

Individual differences: human PFC

Answer 30

Number of internet friends related to grey matter density in various brain regions (Kanai et al, 2011).

Question 31

Individual differences: social group size vs. PFC

Answer 31

Social network size - predicted by orbital PFC cortex volume (Powell et al, 2012).

Path analysis: the directed dependencies among a set of variables.

Dorsal PFC & Orbital PFC -> intentionality; Dorsal PFC, Orbital PFC & intentionality -> network size.

Question 32

Intentionality & culture: intentionality

Answer 32

= the power of minds to be about, to represent or to stand for things, properties and states of affairs.

ToM: ability to attribute mental states to oneself and others.

Intentionality = “advanced ToM”.

Absolute upper limit for non-humans = 2.

Human adults (minimum level required for religion) = 4 (Dunbar, 2003).

Stiller & Dunbar (2007): intentionality measured as the level at which participants failed ToM questions (M = 5.03).

Question 33

Intentionality & culture: intention to cheat

Answer 33

Tactical deception is correlated to neocortex ratio in primate taxa (Byrne & Corp, 2004).

Cheating only achievable when one understands other individual’s mind.

Question 34

Intentionality & culture: Tomasello’s work

Answer 34

Individual intentionality: personal goal-directed behaviour.
- requires high level of cognitive functioning.

Collective intentionality: conventions and norms built on cultural common ground.

Requires engaging in complex social interactions.
- development of collective intentionality gives rise to human cultures.

Question 35

Intentionality & culture: individual intentionality

Answer 35

Tomasello et al (2005):

Goal -> decision making -> intention -> action

Decision making also related to attention -> action, reality and result.

Question 36

Intentionality & culture: joint intentionality

Answer 36

Joint/shared - individuals collaborate in accomplishing a common goal (Tomasello et al, 2005).

Question 37

Intentionality & culture: Tomasello’s work

Answer 37

Argues joint/shared intentionality is the origin of human culture.

Collaboration does not equal cooperation.

• cooperation = each individual does a part but does not interact to produce final product.
• collaboration = link together as networked minds committed to the outcome.

Question 38

Intentionality & culture: shared intentionality

Answer 38

Collaboration requires high level of shared intentionality - Tomasello (2001/04).

Chimps can point imperatively (to get food) but not declaratively (help find something).

Chimps cannot understand helping behaviour.

• helpers looking in two barrels and pointing at one with food in (Tomasello et al, 2003).
• human children have this ability since 1 year (T, 1999).

Question 39

Intentionality & culture: what’s unique about humans?

Answer 39

Sharing intentionality requires high level of intentionality.
- humans capable, other primates not (Dunbar, 2003; Stiller & Dunbar, 2007).

Human children and chimps have similar cognitive skills for physical world, but humans are better dealing with social world.
- “cultural intelligence hypothesis” (Hermann et al, 2007) - humans have cognitive skills not possessed by other primates for participating in cultural groups.

Tomasello argues that human thinking is fundamentally collaborative and based on joint intentionality, whereas other primates thinking is competitive and based on individual intentionality.
- “shared intentionality hypothesis” (Tomasello et al, 2005) - states distinctive nature of human cooperation is due to behavioural differences produced by the presence of these abilities in human lineage.

Question 40

Intentionality & culture: developing shared intentionality

Answer 40

Evolution: individual intentionality -> joint intentionality -> collective intentionality.

Stage 1: individual-joint:

• started from small scale dyadic collaboration in hunting and scavenging which created shared goals and joint attention (gaze following).
• more collaborative = more successful hunters and attractive mates -> more offspring -> evolutionary success.

Stage 2: joint-collective:

• as human populations began growing and competing group life became a collaborative activity.
• this created a much larger and more permanent shared world -> i.e. culture.
• language developed during this stage (Tomasello, 2010) from the basis of gestures and pointing.

Question 41

Intentionality & culture: cumulative culture

Answer 41

Human culture can cumulate over generations, but not in monkeys and apes.

Only observed in human children: teaching, communication, observational, learning, imitation, pro-sociality (Dean et al, 2012).

Question 42

Criticisms & questions: only theories

Answer 42

Many arguments lack empirical evidence.

E.G:

• group size limit in hominoid primates.
• the origin of culture.
• origin of human communication.

Question 43

Criticisms & questions: embodied cognition

Answer 43

Social brain hypothesis follows cartesian dualism: mind vs. matter.
- whilst different substances, causally interact.

Embodied cognition = not only shaped by brain (matter) but also by ming-matter interactions.

More attention needed for environment (Barrett et al, 2007).

Question 44

Criticisms & questions: social insects?

Answer 44

Brains much smaller than humans are also known to support social relationships.
- eg. social insect hierarchies -> paper wasp.